191 Speed of light from galaxies. Refer to The Astronomical Journal study of galaxy velocities, presented in Exercise 186 .

A second cluster of galaxies, named A1775, is thought to be a double cluster —that is, two clusters of galaxies in close proximity. Fifty-one velocity observations (in kilometers per second, km/s) from cluster A1775 are listed in the table on the next page. The data are saved in the GALAXY2 file.\

a. Use a graphical method to describe the velocity distribution of galaxy cluster A1775.

b. Examine the graph you created in part a . Is there evidence to support the double-cluster theory? Explain.

c. Calculate numerical descriptive measures (e.g., mean and standard deviation) for galaxy velocities in cluster A1775. Depending on your answer to part b , you may need to calculate two sets of numerical descriptive measures, one for each of the clusters (say, A1775A and A1775B) within the double cluster.

d. Suppose you observe a galaxy velocity of 20,000 km/s.
Is this galaxy likely to belong to cluster A1775A or A1775B? Explain.

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Data for Exercise 191 18,792 21,993 23,059 19,462 19,057 23,017 22,922 20,210 21,911 19,225 20,785 22,781 23,303 22,192 20,186 23,292 19,408 24,909 19,866 22,891 23,121 19,673 23,261 22,796 22,355 19,807 23,432 22,625 22,744 22,426 19,111 18,933 22,417 19,595 23,408 22,809 19,619 22,738 18,499 19,130 23,220 22,647 22,718 22,779 19,026 22,513 19,740 22,682 19,404 22,193 19,179 Based on Oegerle, W. R., Hill, J. M., and Fitchett, M. J. "Observations of high dispersion clusters of galaxies: Constraints on cold dark matter." The Astronomical Journal, Vol. 110, No. 1, July 1995, (Table 1 and Figure 1).